The encoding of objects is a field of great interest from the point of view of their classification and identification. The most widespread methods of encoding are bar codes, radiofrequency circuits (RFID) and magnetic materials. In each of these methods the codes have the corresponding reader associated.
Bar codes are read by passing a small point of laser light over the printed bar code symbol. The darks bars absorb the light source from the scanner and this is reflected in the luminous spaces. The function of the scanner is to read the bar code symbol and provide the computer with an electrical output corresponding to the bars and spaces of the bar code. It is the decoder, however, that recognizes the bar code symbols, analyzes the content of the read bar code and transmits these data to the computer in a traditional data format. Examples of this technology may be found in United States patent application US-A1-2005/236486 or in the U.S. Pat. No. 6,227,450 or U.S. Pat. No. 5,484,992.
As their active element, radiofrequency labels have an LC circuit (inductance-condenser) and are activated by means of an electromagnetic wave whose frequency coincides with the resonance frequency of the circuit. A receiving antenna detects the presence of the circuit activated. In the case of the simplest labels encoding is done by varying the circuit impedance: in the more complex cases the LC circuit is connected to a chip containing information.
Conventional magnetic labels have the information on a magnetic carrier. Until now labels of this type have been activated by an alternating magnetic field and their detection carried out by electromagnetic induction.
A soft magnetic material is characterized in that it is magnetized in the presence of an alternating magnetic field and it is demagnetized constantly according to the direction of the field applied. The hysteresis loop of each material gives account of this behavior.
Amorphous magnetic materials exhibit optimum properties as soft magnetic elements and, in particular, they have a property known as ferromagnetic resonance. In particular, magnetic wires and microwires have an easy magnetization axis in their longitudinal direction. When a low-frequency magnetic field is applied, its magnetization is oriented in this longitudinal direction and precesses with a frequency of its own around the easy axis.